Four quadrant bidirectional switch

ABSTRACT

A four quadrant bidirectional switch. In one embodiment, the four quadrant bidirectional switch comprises a first switch, a second switch, and a third switch, wherein (i) the first and second switches are normally-off switches, (ii) the third switch is a dual-gate, bidirectional, normally-on switch, and (iii) the first, the second, and the third switches are coupled to one another in a bi-cascode configuration.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent applicationSer. No. 61/484,582, filed May 10, 2011, which is herein incorporated inits entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to a bidirectional switch, inparticular to a fully controlled, four quadrant, bidirectional switch.

2. Description of the Related Art

Fully controlled bidirectional power switches may be utilized in devicessuch as AC-AC matrix converters to provide the converters with higheroperating efficiencies as compared to conventional DC-linked AC-ACconverters.

A fully controlled four quadrant bidirectional switch can beimplemented, for example, using two insulated gate bipolar transistors(IGBTs) in antiparallel along with two diodes in series, or utilizingtwo source-connected high-voltage metal-oxide-semiconductor field-effecttransistors (MOSFETS). However, such solutions suffer from drawbackssuch as high conduction loss and may be limited to relatively lowfrequencies (e.g., less than 50 kHz).

Therefore, there is a need in the art for an efficient fully controlled,four quadrant bidirectional switch.

SUMMARY OF THE INVENTION

Embodiments of the present invention generally relate to a four quadrantbidirectional switch. In one embodiment, the four quadrant bidirectionalswitch comprises a first switch, a second switch, and a third switch,wherein (i) the first and second switches are normally-off switches,(ii) the third switch is a dual-gate, bidirectional, normally-on switch,and (iii) the first, the second, and the third switches are coupled toone another in a bi-cascode configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a schematic diagram of a bidirectional power switch inaccordance with one or more embodiments of the present invention;

FIG. 2 is a cross-sectional view of a structure of a switch inaccordance with one or more embodiments of the present invention;

FIG. 3 is a four quadrant voltage-current plane graph depicting draincharacteristics of the switch in accordance with one or more embodimentsof the present invention;

FIG. 4 is a block diagram of a system for power conversion comprisingone or more embodiments of the present invention;

FIG. 5 a is a schematic diagram of a bidirectional power switch inaccordance with one or more alternative embodiments of the presentinvention

FIG. 5 b is a schematic diagram of a bidirectional power switch inaccordance with one or more alternative embodiments of the presentinvention; and

FIG. 6 is a cross-sectional view of a structure of a switch inaccordance with one or more alternative embodiments of the presentinvention.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of a bidirectional power switch 100 inaccordance with one or more embodiments of the present invention. Thebidirectional power switch 100, also referred to as “switch 100”, is afully controlled, four quadrant bidirectional power switch. The switch100 comprises switches 102, 104, and 106. The switches 102 and 104 areeach normally-off field effect transistors (FETs), such as low-voltage(generally less than or equal to 30 volts) siliconmetal-oxide-semiconductor field-effect transistors (MOSFETS), and theswitch 106 is a single normally-on dual gate bidirectional switch. Theswitches 102, 106, and 104 are coupled in a bi-directional cascade, orbi-cascode, configuration, where a drain terminal 102-D of the switch102 is coupled to a first source terminal 106-S1 of the switch 106, anda second source terminal 106-S2 of the switch 106 is coupled to a drainterminal 104-D of the switch 104. A source terminal 102-S of the switch102 is coupled to a first gate terminal 106-G1 of the switch 106, and asecond gate terminal 106-G2 of the switch 106 is coupled to a sourceterminal 104-S of the switch 104.

The switch 102 has a body diode 108 coupled across its source terminal102-S and drain terminal 102-D, where an anode terminal of the bodydiode 108 is coupled to the source terminal 102-S and a cathode terminalof the body diode 108 is coupled to the drain terminal 102-D. The switch104 has a body diode 110 coupled across its source terminal 104-S anddrain terminal 104-D, where an anode terminal of the body diode 110 iscoupled to the source terminal 104-S and a cathode terminal of the bodydiode 110 is coupled to the drain terminal 104-D.

The switches 102 and 104 may be commercially-available low-voltageMOSFETs having very low on-resistance. In one embodiment, the switches102 and 104 may be low conduction loss, low-voltage n-channelenhancement mode silicon MOSFETS, such as Infineon Technology'sBSC050NE2LS, 5 mOhm on-resistance, 25V MOSFET.

The switch 106 is a dual-gate normally-on switch which may befabricated, for example, using a wide bandgap semiconductor materialsuch as an aluminum gallium nitride/gallium nitride (AlGaN/GaN) materialsystem, silicon carbide (SiC), or similar materials having a largerbandgap and hence larger critical electric field than silicon. In oneembodiment, the switch 106 is a dual-gate, low conduction loss, smallarea (for example at blocking voltage (BV)=1200V, RDSon*Area<5∴10⁻³ Ohmcm²), bidirectional, normally-on, high-voltage (blocking voltage greaterthan 800V) switch fabricated using a AlGaN/GaN based High ElectronMobility Transistor (HEMT) structure as described in detail below withrespect to FIG. 2.

FIG. 2 is a cross-sectional view of a structure of a switch 106 (havingfor example blocking voltage=1200V, on-resistance=0.1 Ohm andarea=3×10⁻³ cm²) in accordance with one or more embodiments of thepresent invention. The switch 106 comprises layers 202, 204, 206 and208, with the source terminals 106-S1/106-S2 and gate terminals106-G1/106-G2 coupled to the layer 208. The source terminals aretypically thin metal layers with composition known in the art to makeohmic contact to layer 208, and the gate terminals are typically thinmetal layers with composition known in the art that produces a Schottkycontact to layer 208. The layer 202 is a substrate, such as GaN, SiC,Al₂O₃ (Aluminum oxide), or silicon, generally with thickness of 200microns or more. A buffer layer between layers 202 and 204 mayoptionally be present depending on the type of substrate that is used.

The layer 204 is a GaN layer sandwiched between the layer 202 and thelayer 208, which is an AlGaN layer. Layer 208 will generally have athickness of less than 1 micron and is commonly in the range of 0.02 to0.2 microns. Also, layer 208 may have an aluminum composition, x,ranging from x=0.01 to 1 where the composition is designated as inAl_(x)Ga_(1-x)N, The layer 206 is a two-dimensional electron gas (2DEG)layer formed between layers 204 and 208, i.e, a thin layer of highlymobile conducting electrons (electron mobility of 1100 cm²/Vs or more)with very high concentration (electron sheet concentration of 10¹³ cm⁻²or more), giving the channel very low resistivity. A voltage applied toeither of the gates 106-G1 or 106-G2 alters the conductivity of thislayer. The thickness of layer 204 will generally be more than 2 micronsand commonly 6 microns or more depending on the blocking voltage of thedevice. The thickness of this layer must be increased the higher theblocking voltage of the device. The separation distance between the gateterminals 106-G1 and 106-G2 also affects the blocking voltage capabilityof the device with increased separation distance needed for increasedblocking voltage. For example the 106-G1 to 106-G2 separation distancewill generally be more than 5 microns and commonly 15-30 microns forAlGaN/GaN based devices ranging from 800V to 1200V. The separationdistance between the source and gate terminals at each end of the device(i.e., 106-S1 to 106-G1 and 106-S2 to 106-G2) can be much smaller,generally 0.5 to 2 microns, without effecting the blocking voltage ofthe device.

The gate terminals 106-G1 and 106-G2 are insulated and hence have verylow leakage current, for example on the order of 100 nA/mm or less. Thegate control characteristics may be manufactured with tight tolerance onthe threshold voltage and can tolerate a range of control voltages, forexample maximum gate voltage relative to source “VGS” of +2V and minimum“VGS” of −10V, without degradation.

The relatively small chip area of the switch 106, for example on theorder of 20 times smaller than an analogous silicon-based device,enables the switch 106 to have lower parasitic capacitance (more than10× lower compared to an analogous silicon-based device) and hence lowerdynamic switching power loss, allows a higher operating frequency (morethan 10× higher compared to an analogous silicon-based device), reducescost of the chip and enables a smaller size circuit board.

FIG. 3 is a four quadrant voltage-current plane graph 300 depictingdrain characteristics of the switch 106 in accordance with one or moreembodiments of the present invention. The dual-gate normally-on switch106 is controlled by the voltage present from gate to source as depictedin the graph 300, i.e., the voltage from gate 106-G1 to source 106-S1(shown as VG1S1), and the voltage from gate 106-G2 to source 106-S2(shown as VG2S2). The gate-to-source values depicted in the graph 300are representative of one embodiment of the switch 106.

FIG. 4 is a block diagram of a system 400 for power conversioncomprising one or more embodiments of the present invention. Thisdiagram only portrays one variation of the myriad of possible systemconfigurations and devices that may utilize the present invention. Thepresent invention can be utilized in any system or device requiring afully controlled, four quadrant, bidirectional switch.

The system 400 comprises a plurality of power converters 402-1, 402-2,402-3 . . . 402-N, collectively referred to as power converters 402; aplurality of DC power sources 404-1, 404-2, 404-3 . . . 404-N,collectively referred to as DC power sources 404; a system controller406; a bus 408; and a load center 410. The DC power sources 404 may beany suitable DC source, such as an output from a previous powerconversion stage, a battery, a renewable energy source (e.g., a solarpanel or photovoltaic (PV) module, a wind turbine, a hydroelectricsystem, or similar renewable energy source), or the like, for providingDC power.

Each power converter 402-1, 402-2, 402-3 . . . 402-N is coupled to asingle DC power source 404-1, 404-2, 404-3 . . . 404-N, respectively; insome alternative embodiments, multiple DC power sources 404 may becoupled to a single power converter 402, for example a singlecentralized power converter 402. Each of the power converters 402comprises at least one bidirectional power switch 100 (e.g., the powerconverters 402-1, 402-2, 402-3 . . . 402-N comprise the bidirectionalpower switches 100-1, 100-2, 100-3 . . . 100-N, respectively) utilizedduring power conversion. In some embodiments, the power converters 402may be resonant power converters comprising cycloconverters that employthe bidirectional power switch 100.

The power converters 402 are coupled to the system controller 406 viathe bus 408. The system controller 406 is capable of communicating withthe power converters 402 by wireless and/or wired communication forproviding operative control of the power converters 402. The powerconverters 402 are further coupled to the load center 410 via the bus408.

The power converters 402 are each capable of converting the received DCpower to AC power, although in other embodiments the power convertersmay receive an AC input and convert the received input to a DC output.The power converters 402 couple the generated output power to the loadcenter 410 via the bus 408. The generated power may then be distributedfor use, for example to one or more appliances, and/or the generatedenergy may be stored for later use, for example using batteries, heatedwater, hydro pumping, H₂O-to-hydrogen conversion, or the like. In someembodiments, the power converters 402 convert the DC input power to ACpower that is commercial power grid compliant and couple the AC power tothe commercial power grid via the load center 410.

In some alternative embodiments, the power converters 402 may be DC-DCpower converters; in other alternative embodiments, the power converters402 may receive an AC input and be AC-AC converters (e.g., AC-AC matrixconverters).

FIG. 5 a is a schematic diagram of a bidirectional power switch 500 inaccordance with one or more alternative embodiments of the presentinvention. The bidirectional power switch 500, also referred to as“switch 500”, may be implemented on a single substrate as describedfurther below with respect to FIG. 6. Analogous to the switch 100, theswitch 500 is a fully controlled, four quadrant bidirectional powerswitch. The switch 500 comprises switches 502, 504, and 506. In oneembodiment, the switches 502 and 504 are each normally-off galliumnitride (GaN) High Electron Mobility Transistors (HEMTs), and the switch106 is a single high-voltage (blocking voltage >800V) dual-gatenormally-on GaN HEMT, having low on-state resistance and small area, forexample a 1200V rated device would have RDSon*Area<5×10⁻³ Ohm cm². Theswitches 502, 506, and 504 are coupled in a bi-directional cascode, orbi-cascode, configuration, where a drain terminal 502-D of the switch502 is coupled to a first source terminal 506-S1 of the switch 506, anda second source terminal 506-S2 of the switch 506 is coupled to a drainterminal 504-D of the switch 504. A source terminal 502-S of the switch502 is coupled to a first gate terminal 506-G1 of the switch 506, and asecond gate terminal 506-G2 of the switch 506 is coupled to a sourceterminal 504-S of the switch 504.

In FIG. 5 a, the switches 502 and 504 are shown without anti-paralleldiodes between the source and drain terminals of either switch 502 or504. Proper operation in the on-state of this embodiment of thebidirectional switch 500 requires that both switches 502 and 504 beturned on when conducting a positive current or a negative current.

FIG. 5 b is a schematic diagram of a bidirectional power switch 500 inaccordance with one or more alternative embodiments of the presentinvention. As depicted in FIG. 5 b, diode D1 is present across the drainand source terminals 502-D and 502-S of switch 502, with cathode D1-Ctied to drain terminal 502-D and anode D1-A tied to 502-S, and diode D2is present across the drain and source terminals 504-D and 504-S ofswitch 504, with cathode D2-C tied to drain terminal 504-D and anodeD2-A tied to source terminal 504-S. This embodiment no longer has therestriction that both switches 502 and 504 must be in their conductingstate for proper operation in the on-state of the bi-directional switch500. For example, if positive current enters through the top terminal(504-S), switch 504 may either be on or off while switch 502 must be on.In this case, if switch 504 is off then diode D2 will conduct and allowcurrent to flow. Likewise, if positive current enters through the bottomterminal (502-S), switch 502 may either be on or off while switch 504must be on. In this case, if switch 502 is off then diode D1 willconduct and allow current to flow.

FIG. 6 is a cross-sectional view of a structure of a switch 500 inaccordance with one or more alternative embodiments of the presentinvention. The switch 500 comprises layers 602, 604, 606 and 608. Sourceterminals 502-S and 504-S as well as the gate terminals 502-G, 504-G,506-G1 and 506-G2 are coupled to the layer 608. The source terminals502-S and 504-S are typically thin metal layers with composition knownin the art to make ohmic contact to layer 608, The gate terminals 506-G1and 506-G2 are typically thin metal layers with composition known in theart that produces a Schottky contact to layer 608 and gate terminals502-G and 504-G are typically of material known in the art to make theadjacent (below) 2DEG region devoid of electrons (non-conducting) withzero bias voltage on the gate and conducting with positive bias voltageon the gate. The layer 602 is a substrate, such as GaN, SiC, Al₂O₃(Aluminum oxide), or silicon, generally with thickness of 200 microns ormore. A buffer layer between layers 602 and 604 may optionally bepresent depending on the type of substrate that is used.

The layer 604 is a GaN layer sandwiched between the layer 602 and thelayer 608, which is an AlGaN layer. Layer 608 will generally have athickness of less than 1 micron and is commonly in the range of 0.02 to0.2 microns. Also, layer 608 may have an aluminum composition, x,ranging from x=0.01 to 1 where the composition is designated as inAl_(x)Ga_(1-x)N. The layer 606 is a two-dimensional electron gas (2DEG)layer formed between layers 604 and 608, i.e., a thin layer of highlymobile conducting electrons (electron mobility of 1100 cm²/Vs or more)with very high concentration (electron sheet concentration of 10¹³ cm⁻²or more), giving the channel very low resistivity. A voltage applied toany of the gates 502-G, 504-G, 506-G1 or 506-G2 alters the conductivityof this layer. The thickness of layer 604 will generally be more than 2microns and commonly 6 microns or more depending on the blocking voltageof the device. The thickness of this layer must be increased the higherthe blocking voltage of the device. The separation distance between thegate terminals 506-G1 and 506-G2 also affects the blocking voltagecapability of the device with increased separation distance needed forincreased blocking voltage. For example the 106-G1 to 106-G2 separationdistance will generally be more than 5 microns and commonly 15-30microns for AlGaN/GaN based devices ranging from 800V to 1200V. Theseparation distance between the source and gate terminals at each end ofthe device (i.e., 502-S to 502-G, 502-G to 506-G1, 504-S to 504-G, and504-G to 506-G2) can be much smaller, generally 0.5 to 2 microns,without effecting the blocking voltage of the device.

The foregoing description of embodiments of the invention comprises anumber of elements, devices, circuits and/or assemblies that performvarious functions as described. These elements, devices, circuits,and/or assemblies are exemplary implementations of means for performingtheir respectively described functions.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. A four quadrant bidirectional switchcomprising: a bidirectional power switch having a first switch, a secondswitch, and a third switch, wherein (i) the first and second switchesare normally-off switches, (ii) the third switch is a dual-gate,bidirectional, normally-on switch, and (iii) the first, the second, andthe third switches are coupled to one another in a bi-cascodeconfiguration; and wherein the bidirectional power switch operates ineach quadrant of a four quadrant voltage-current plane.
 2. The fourquadrant bidirectional switch of claim 1, wherein the first and secondswitches are silicon metal-oxide-semiconductor field-effect transistors(MOSFETS).
 3. The four quadrant bidirectional switch of claim 2, whereinthe first and second switches are n-channel enhancement mode switches.4. The four quadrant bidirectional switch of claim 1, wherein the thirdswitch comprises a wide bandgap semiconductor material.
 5. The fourquadrant bidirectional switch of claim 4, wherein the wide bandgapsemiconductor material is aluminum gallium nitride/gallium nitride(AlGaN/GaN).
 6. The four quadrant bidirectional switch of claim 5,wherein the third switch employs a High Electron Mobility Transistor(HEMT) structure.
 7. The four quadrant bidirectional switch of claim 1,wherein the bidirectional power switch is implemented on a singlesubstrate.
 8. A power conversion system, comprising: a power convertercomprising a bidirectional power switch comprising a first switch, asecond switch, and a third switch, wherein (i) the first and secondswitches are normally-off switches, (ii) the third switch is adual-gate, bidirectional, normally-on switch, and (iii) the first, thesecond, and the third switches are coupled to one another in abi-cascode configuration; and wherein the bidirectional power switchoperates in each quadrant of a four quadrant voltage-current plane. 9.The power conversion system of claim 8, wherein the first and secondswitches are silicon metal-oxide-semiconductor field-effect transistors(MOSFETS).
 10. The power conversion system of claim 9, wherein the firstand second switches are n-channel enhancement mode switches.
 11. Thepower conversion system of claim 8, wherein the third switch comprises awide bandgap semiconductor material.
 12. The power conversion system ofclaim 11, wherein the wide bandgap semiconductor material is aluminumgallium nitride/gallium nitride (AlGaN/GaN).
 13. The power conversionsystem of claim 12, wherein the third switch employs a High ElectronMobility Transistor (HEMT) structure.
 14. The power conversion system ofclaim 8, wherein the bidirectional power switch is implemented on asingle substrate.
 15. The power conversion system of claim 8, whereinthe power converter is a resonant converter.
 16. The power conversionsystem of claim 8, wherein the power converter is a DC-DC converter. 17.The power conversion system of claim 8, wherein the power converter is aDC-AC inverter.
 18. The power conversion system of claim 8, wherein thepower converter is an AC-AC converter.
 19. The power conversion systemof claim 8, wherein the power converter receives a DC input from arenewable energy source.
 20. The power conversion system of claim 19,wherein the renewable energy source is a photovoltaic (PV) module.